The object of this research is to learn more about the control of ventilation in the regulation of carbon dioxide and oxygen concentrations. C 2(t) and O2(t) can be considered as two time varying biological signals. There is much information (e.g., respiratory period, time of inspiration, metabolic rate of CO2 production and O2 utilization, etc..) coded on these signals. It is our aim to determine: 1. what information the body uses in the feedback regultion of CO2(t) and O2(t), 2. where it is sensed (receptors) 3. the dynamics of how this information interacts to determine the rate and depth of breathing. For this work we have developed an experimental animal Preparation in which we can independently force the gas concentrations in the lung as an input variable and measure the rate and depth of respiration as an output variable. This preparation is the unidirectionally ventilated chicken. This independent or open loop forcing of gas cocentration in the lung is accomplished by keeping a fast constant pressure air stream flowing thru the bird and manipulating the gas concentration of that stream. BIBLIOGRAPHIC REFERENCES: Kunz, A.L. and D.A. Miller. "Pacing of Avian Respiration With CO2 Oscillation". Respir. Physiol., 22:167-177. 1974. Kunz, A.L. and D.A. Miller. "Effects of Feedback Delay Upon the Apparent Damping Ratio of Avian Respiratory Control System", Respir. Physiol., 22: 179-189, 1974.